A systematic study on the presence of bottlenose dolphins (Tursiops truncatus) in the Río Negro Estuary (RNE), Patagonia Argentina, was carried out between the months March – July from 2008 to 2011. Data ... [more ▼]

A systematic study on the presence of bottlenose dolphins (Tursiops truncatus) in the Río Negro Estuary (RNE), Patagonia Argentina, was carried out between the months March – July from 2008 to 2011. Data on the dolphin’s activity patterns were gathered via an Ad Libitum focal group sampling mode accompanying dorsal fin images taken for identification and re-identification of individuals. A total effort of 188 h resulted in 58 h of positive observation of 124 dolphin groups (sightings per unit effort (SPUE) = 0.66 groups/h). Data analysis showed two main activity states for the observed groups, travelling (65%) and foraging (26%). The remaining 9% of the groups were involved in other activity states. The photo-identification effort, which started opportunistically in 2006, resulted in a catalogue of 21 individual dolphins, with a total mean re-identification rate of 9 days (max = 24 days). When comparing these pictures to the existing catalogue of Bahía San Antonio (approximately 200 km west from the study area) dorsal fins of 20 individuals could be positively matched and most (n = 17) could be subsequently re-identified in both areas, indicating their long distance movements along the North Patagonian coast during the austral autumn months. This season coincides with the lowest amount of feeding activity observed in Bahía San Antonio. This study suggests that bottlenose dolphins enter RNE, mainly during autumn, to forage. It appears that the search for food resources may be the trigger for their movement patterns along the North Patagonian coast during this season, at least for certain individuals. More research is needed to accurately confirm this hypothesis. [less ▲]

In this article, we propose a robust statistical approach to select an appropriate error distribution, in a classical multiplicative heteroscedastic model. In a first step, unlike to the traditional ... [more ▼]

In this article, we propose a robust statistical approach to select an appropriate error distribution, in a classical multiplicative heteroscedastic model. In a first step, unlike to the traditional approach, we don't use any GARCH-type estimation of the conditional variance. Instead, we propose to use a recently developed nonparametric procedure (Mercurio and Spokoiny, 2004): the Local Adaptive Volatility Estimation (LAVE). The motivation for using this method is to avoid a possible model misspecification for the conditional variance. In a second step, we suggest a set of estimation and model selection procedures (Berk-Jones tests, kernel density-based selection, censored likelihood score, coverage probability) based on the so-obtained residuals. These methods enable to assess the global fit of a set of distributions as well as to focus on their behavior in the tails, giving us the capacity to map the strengths and weaknesses of the candidate distributions. A bootstrap procedure is provided to compute the rejection regions in this semiparametric context. Finally, we illustrate our methodology throughout a small simulation study and an application on three time series of daily returns (UBS stock returns, BOVESPA returns and EUR/USD exchange rates) [less ▲]

Palaeoecological and archaeological studies have demonstrated that human populations have long inhabited the moist forests of central Africa. However, spatial and temporal patterns of human activities ... [more ▼]

Palaeoecological and archaeological studies have demonstrated that human populations have long inhabited the moist forests of central Africa. However, spatial and temporal patterns of human activities have hardly been investigated with satisfactory accuracy. In this study, we propose to characterize past human activities at local scale by using a systematic quantitative and qualitative methodology based on soil charcoal and charred botanical remains. A total of 88 equidistant test-pits were excavated along six transects in two contrasting forest types in southern Cameroon. Charred botanical remains were collected by water-sieving and sorted by type (wood charcoals, oil palm endocarps, and unidentified seeds). A total of 50 Accelerator Mass Spectrometry 14C dates were also obtained. Results showed that charred macroremains were found at multiple places in the forest, suggesting scattered human activities, which were distributed into two main periods (Phase A: 2300-1300 BP – Phase B: 580 BP to the present). Charred botanical remains indicated two types of land use: (i) domestic, with oil palm endocarps most often associated with potsherds (villages) and (ii) agricultural, with charcoal as probable remnant of slash-and-burn cultivation (fields). Oil palm endocarp abundance decreased with distance from the identified human settlements. Our methodology allowed documenting, at high resolution, the spatial and temporal patterns of human activities in central African moist forests and could be applied to other tropical contexts. [less ▲]